[PATCH] freepgt: free_pgtables use vma list

Recent woes with some arches needing their own pgd_addr_end macro; and 4-level
clear_page_range regression since 2.6.10's clear_page_tables; and its
long-standing well-known inefficiency in searching throughout the higher-level
page tables for those few entries to clear and free: all can be blamed on
ignoring the list of vmas when we free page tables.

Replace exit_mmap's clear_page_range of the total user address space by
free_pgtables operating on the mm's vma list; unmap_region use it in the same
way, giving floor and ceiling beyond which it may not free tables.  This
brings lmbench fork/exec/sh numbers back to 2.6.10 (unless preempt is enabled,
in which case latency fixes spoil unmap_vmas throughput).

Beware: the do_mmap_pgoff driver failure case must now use unmap_region
instead of zap_page_range, since a page table might have been allocated, and
can only be freed while it is touched by some vma.

Move free_pgtables from mmap.c to memory.c, where its lower levels are adapted
from the clear_page_range levels.  (Most of free_pgtables' old code was
actually for a non-existent case, prev not properly set up, dating from before
hch gave us split_vma.) Pass mmu_gather** in the public interfaces, since we
might want to add latency lockdrops later; but no attempt to do so yet, going
by vma should itself reduce latency.

But what if is_hugepage_only_range?  Those ia64 and ppc64 cases need careful
examination: put that off until a later patch of the series.

What of x86_64's 32bit vdso page __map_syscall32 maps outside any vma?

And the range to sparc64's flush_tlb_pgtables?  It's less clear to me now that
we need to do more than is done here - every PMD_SIZE ever occupied will be
flushed, do we really have to flush every PGDIR_SIZE ever partially occupied? 
A shame to complicate it unnecessarily.

Special thanks to David Miller for time spent repairing my ceilings.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Hugh Dickins
2005-04-19 13:29:15 -07:00
committed by Linus Torvalds
parent 9f6c6fc505
commit e0da382c92
5 changed files with 141 additions and 155 deletions

View File

@ -187,45 +187,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, pmd_t *pmd, int wri
}
/*
* Same as generic free_pgtables(), except constant PGDIR_* and pgd_offset
* are hugetlb region specific.
* Do nothing, until we've worked out what to do! To allow build, we
* must remove reference to clear_page_range since it no longer exists.
*/
void hugetlb_free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *prev,
unsigned long start, unsigned long end)
{
unsigned long first = start & HUGETLB_PGDIR_MASK;
unsigned long last = end + HUGETLB_PGDIR_SIZE - 1;
struct mm_struct *mm = tlb->mm;
if (!prev) {
prev = mm->mmap;
if (!prev)
goto no_mmaps;
if (prev->vm_end > start) {
if (last > prev->vm_start)
last = prev->vm_start;
goto no_mmaps;
}
}
for (;;) {
struct vm_area_struct *next = prev->vm_next;
if (next) {
if (next->vm_start < start) {
prev = next;
continue;
}
if (last > next->vm_start)
last = next->vm_start;
}
if (prev->vm_end > first)
first = prev->vm_end;
break;
}
no_mmaps:
if (last < first) /* for arches with discontiguous pgd indices */
return;
clear_page_range(tlb, first, last);
}
void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, unsigned long end)